It is known to attach various attachments to rotary drive tools. One such attachment is a circular cup-shaped saw blade attached to a power drill or the like for cutting holes in a variety of materials. An arbor arrangement is used to affix the saw blade to a pilot bit, positioned in the center of the cup saw blade, and to permit the blade and pilot bit to be locked into the chuck of the power drill.
Prior art arbor arrangements comprise a body through which the pilot bit extends. The pilot bit extends through a hole in the center of the cup saw blade. A threaded end of the bit is secured to the body using a nut. Typically, at least one pair of pins extend from the top of the body for engaging corresponding holes in the base of the cup saw blade to transfer torque to drive the saw blade. Should the blade jam up during cutting, the pins are particularly susceptible to breakage.
Further, in most cases, the hole in the base of the saw blade is threaded for engagement with a threaded portion on the top of the arbor body. The relatively small number of threads are easily stripped, particularly if uneven force is applied to the drill during cutting. Further, uneven force by the user and wobble, as a result of worn threads, may cause the pins to wear the corresponding holes resulting in greater instability and wear.
Others have attempted to improve the transfer of torque to the cup saw blade by replacing the pins with a square opening which corresponds to a square body fixed adjacent the chuck end of the pilot bit. A washer is fixed above the square portion of the pilot bit to sandwich the blade between the pilot bit and a nut. The chuck end of the pilot bit is then inserted into the chuck of the drill. While improving transfer of torque to the cup saw blade, this prior art arrangement requires a wrench to lock the blade and does not provide any additional locking aspects to ensure that the nut does not back off which can result in loosening of the saw blade relative to the pilot bit.
For the foregoing reasons, there is a need for an improved arbor apparatus for mounting attachments to rotary drive tools. The present invention is directed to this need.